Heart Nerves May Predict Arrhythmia Risk

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This study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

A simple risk score that includes the heart's sympathetic innervation activity might better identify heart failure patients who are at low risk of sudden death and won't benefit from an implantable-cardioverter defibrillator (ICD).

Point out that three independent predictors of sudden cardiac death among heart failure patients were heart/mediastinum ratio (HMR) <1.6, left ventricular ejection fraction (LVEF) <25%, and systolic blood pressure <120 mm Hg.

BALTIMORE -- A simple risk score that includes the heart's sympathetic innervation activity might better identify heart failure patients who are at low risk of sudden death and won't benefit from an implantable-cardioverter defibrillator (ICD), researchers said.

Cardiac MIBG scintigraphic imaging assesses sympathetic nerve activity, measured by the heart-to-mediastinum ratio (HMR), which was found to be useful in predicting heart failure risk in the ADMIRE-HF trial, according to Firas Al Badarin, MD, of Saint Luke's Mid America Heart Institute in Kansas City, and colleagues.

MIBG, also known as lobenguane (AdreView), is a radiotracer labeled with I-123. It is FDA approved for the detection of primary or metastatic pheochromocytoma or neuroblastoma as an adjunct to other diagnostic tests. It is not currently approved for cardiac imaging.

In the current study, researchers found three independent predictors of sudden cardiac death among heart failure patients: HMR <1.6, left ventricular ejection fraction (LVEF) <25%, and systolic blood pressure <120 mmHG, Al Badarin reported here at the annual meeting of the American Society of Nuclear Cardiology (ASNC).

Al Badarin noted that recommendations for ICDs in heart failure patients are primarily based on LVEF, but many people who receive the devices never have life-saving therapy, potentially indicating they have received the device unnecessarily.

In addition, he said that algorithms to predict death from arrhythmias are often complex.

In this study, he and colleagues sought to develop a simple risk stratification score -- the ADMIRE-HF score -- that could help guide the implantation of ICDs.

They identified 778 patients from the ADMIRE-HF trial who did not have ICDs at baseline. Patients had a LVEF <35% and NYHA class II or III. During a median follow-up of 17 months, 25% of patients received an ICD.

Researchers quantified late HMR from planar images of MIBG as a measure of relative myocardial sympathetic nerve activity.

The primary outcome of this study was the first occurrence of serious arrhythmic events, which included a composite of sudden cardiac death, appropriate ICD therapy, resuscitated cardiac arrest, and sustained ventricular tachycardia (>30 seconds).

Al Badarin and colleagues recorded events in 54 patients. When they adjusted for confounders, they found three variables were significantly associated with having an arrhythmic event:

However, HMR by itself is not specific enough to identify those at risk, Al Badarin told MedPage Today. "Even though 90% of patients who experienced an event had a heart-to-mediastinum ratio of less than 1.6, 76% of those without an arrhythmic events also had a ratio below 1.6."

The standard deviations for LVEF and systolic blood pressure, as well, also make each of these two markers not very specific for arrhythmic events. However, using the three of them together to generate an ADMIRE-HF score was highly prognostic, he said.

Those with a score less than 4 had a 2% event rate, compared with a 10% event rate for those with a score between 4 and 15 and a 16% event rate for those with a score higher than 15.

"For those with a low event rate, we might consider delaying the implantation of an ICD," Al Badarin said. "However, more studies are needed to confirm these results."

Interestingly, brain natriuretic peptide levels and LV hypertrophy were significant differences between those with and without arrhythmic events at baseline, but lost their significance after adjusting for potential covariates.

A limitation to the study is the relatively short follow-up and the fact that some patients received an ICD after enrollment, researchers noted. Also, the results may not be generalizable to all primary prevention heart failure patients.

The original ADMIRE-HF study was supported by GE Healthcare, which makes AdreView.

Al Badarin reported no conflicts of interest.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner